1. Field of the Invention
This invention relates to a reproducing apparatus of the kind reproducing information signals recorded in many recording tracks formed at intervals of a predetermined pitch on a record bearing medium.
2. Description of the Prior Art
In the present specification, VTR's of the rotary two-head type arranged to perform tracking by the known four-frequency pilot method are described as typical examples of the apparatuses of the above-stated kind.
Briefly stated, the VTR of this type is arranged in the following manner for obtaining a tracking control signal during a reproducing operation: FIG. 1 of the accompanying drawings shows a signal layout made on a magnetic tape by the VTR which performs tracking by the four-frequency pilot method. FIG. 2 shows the circuit arrangement including elements essential to the VTR for obtaining a tracking error signal (hereinafter referred to as an ATF signal) by the four-frequency pilot method. Referring to FIG. 1, the illustration includes a magnetic tape 1; an arrow 2 indicating a direction in which the tape 1 is to be allowed to travel; an arrow 3 indicating the tracing direction of a head; tracks A1, A2, A3 which are formed on the tape to have a first magnetizing direction respectively; and tracks B1, B2 and B3 formed to have a second magnetizing direction respectively. Pilot signals having different frequency values f1, f2, f3 and f4 are respectively superimposed on one field portions of a video signal. For example, the frequency values of these pilot signals are arranged to be f1=6.5 fH, f2=7.5 fH, f3=9.5 fH and f4=10.5 fH, wherein fH represents the horizontal scanning frequency employed for the video signal. As apparent from the illustration, the pilot signals of these frequency values are superimposed on the video signal one after another in rotation in the sequence of f1.fwdarw.f2.fwdarw.f4.fwdarw.f3.fwdarw.f1.fwdarw.f2. As a result, the frequency difference between the pilot signals superimposed on adjacent tracks is either fH or 3 fH. Thus, there exist two different degrees of difference between frequency values of the pilot signals superimposed on adjacent tracks. The pilot signals of different degrees of frequency difference are alternately arranged in general. In other words, in case that the pilot signals are generated one after another in the sequence of rotation f1.fwdarw.f2.fwdarw.f4.fwdarw.f3, it suffices to meet the condition of f4-f3=f2-f1 and f3.noteq.f2.
The operation of the circuit arrangement shown in FIG. 2 is as follows: To a terminal 5 is supplied via a reproducing head a video signal which has the pilot signal superimposed thereon. A low-pass filter 6 (hereinafter referred to as LPF) separates the pilot signal component from the video signal. The separate pilot signal is supplied to a multiplier 8. A local pilot signal, which is generated by a local pilot signal generating circuit 7, is also supplied to the multiplier 8. The local pilot signal is arranged to have the same frequency as that of the pilot signal superimposed on the track (the main track) which is mainly traced by the reproducing head. In that instance, a difference between the local pilot signal and each of pilot signal components reproduced from two tracks adjacent to the main track is fH or 3 fH or 3 fH. These differences are respectively taken out by band-pass filters (hereinafter referred to as BPF's) 9 and 10 and are detected by detection circuits 11 and 12, respectively. Then, the output levels of these detection circuits 11 and 12 are compared by a comparator 13. The result of comparison then indicates the degree of deviation of the reproducing head from the main track.
For example, assuming that the reproducing head is now in a position as shown at a position 4a in FIG. 1, the frequency value of the local pilot signal is f4; the difference of the local pilot signal is 3 fH from the pilot signal obtained from a track B1 and is fH from another pilot signal obtained from another track B2. If the position of the reproducing head is at a position 4b as shown in FIG. 1, the frequency value of the local pilot signal is f3 differing by fH and 3 fH respectively from pilot signals obtained from tracks A2 and A3.
As apparent from the example described above, in carrying out a so-called normal reproduction, the differences (in frequency) of the local pilot signal from the pilot signals obtained (or reproduced) from tracks in front of and behind the main track, come to interchange with each other every time the tracing position of the reproducing head shifts from one main tracing track to another. Therefore, the output of the comparator 13 is produced via an inverting amplifier 14 at intervals one field. By this, the ATF signal which indicates the degree and the direction of deviation of the reproducing head from the main track is produced from a terminal 17. The illustration further includes a switching circuit 16; and a terminal 15 receiving a rectangular wave signal which alternately repeats a high level and a low level thereof for every one-field period and is obtained by detecting the rotation of the rotating reproducing head.
The local pilot signal includes four different frequency pilot signals which are produced in rotation. In the case of the normal reproduction, the rotation of these local pilot signal frequency values is of course in the sequence of f1.fwdarw.f2.fwdarw.f4.fwdarw.f3 which is the same as the frequency values of the pilot signals superimposed on the video signal in recording. Therefore, the local pilot signals can be obtained by operating the same pilot signal generating oscillation means which is used for recording in the same manner as in recording.
The tracking error signal (ATF signal), which is mentioned in the foregoing, is usable as it is for reproduction only when the reproduction is the normal reproduction which is to be carried out at the same tape travelling speed as the speed employed for recording. Whereas, in the event of a varied-speed-reproduction operation, wherein reproduction is to be performed by allowing the record bearing medium (or tape) to travel at a speed different from the speed employed for recording, it becomes difficult to correctly select the frequency of the local pilot signal to be generated for the reproducing operation. Other known method of using an ATF signal for tracking control includes methods of sampling and holding the ATF signal. However, these methods have been hindering reduction in size and cost of VTR's as they require complex arrangement of the circuits, etc. of the apparatuses.